Increasingly, functions in motor vehicles are provided as (partially) autonomous driving maneuvers. These currently include in particular the “autonomous parking” and “adaptive cruise control” functions. With the “autonomous parking” function for example, the driver of a vehicle is assisted when maneuvering, in particular during a parking process. During this the surroundings of the vehicle are sensed by means of sensors and the vehicle is automatically braked if it approaches another object too closely, such as for example a parked vehicle. The “adaptive cruise control” function, which enables automatic approaching and braking because of decelerated or stationary vehicles ahead, also operates similarly.
Known driver assistance systems usually comprise a controller with an algorithm, ultrasonic sensors for sensing the surroundings of the vehicle and an actuator of the brake system, such as for example a hydraulic unit. Once the vehicle has fallen below a minimum distance, the actuator is activated by the controller and the vehicle is automatically braked. If the hydraulic brake system now fails during a process—for example because of a fault of the brake actuator or brake controller—the vehicle is no longer automatically braked, so that a collision with another object can occur.
DE102006048910 is known from the prior art for example. Said document discloses a method for protecting a parking assistance system against a failure of the service brake system. In order to avoid a collision of the vehicle with a nearby object, it is proposed to monitor the function of the service brake system and in the event of a fault to operate at least one other vehicle system, such as for example an automatic gearbox or an automatic parking brake, in order to brake the vehicle and/or to interrupt the transfer of the drive torque to the wheels.
Furthermore, DE102010001492 discloses a method for activating at least one electronically activated parking brake device in a vehicle, wherein the parking brake device is used for support depending on engine and/or gearbox parameters in predetermined operative states of the vehicle. A further application area of the procedure is the preparation of a braking process for the vehicle. In particular, with multi-disk brakes, at the start of the braking process when operating the brake pedal only the air gap between the disks is closed. A braking effect does not occur yet here, so that the braking process is delayed. The electronic parking brake device can be activated to reduce or remove the air gap between the disks if a predetermined negative gradient is detected during the operative displacement of the gas pedal. If for example it is determined that the driver has finished the operation of the gas pedal quickly and changed to the brake pedal, the electronic parking brake device can be activated in order to enable faster braking of the vehicle for the driver as a result.
Systems are also known that assist the driver as a traction aid by means of automatic braking when starting off on a hill. For example, DE10218825 discloses a motor vehicle brake system in a preferred development with which activation of the parking function takes place automatically on inclines after reaching the stationary vehicle state from forward travel. In this way, unintended backward rolling of the vehicle is substantially prevented. In one advantageous configuration of the aforementioned embodiment, the activation of the parking function only takes place if the service brake is released. This is based on the consideration that backward rolling of the vehicle cannot occur if the service brake is being operated, so that owing to said configuration unnecessary activation of the parking function is avoided.
If the service brake system fails during an autonomous or partially autonomous function—for example because of a fault of the brake actuator or brake controller—the vehicle will no longer be automatically braked, so that a collision with another object can occur.